The present invention relates to a pressure transducer assembly for measuring differential pressures across a restriction in a pipe carrying process fluids. More particularly, this invention relates to a transducer assembly for making such measurements in small pipes carrying fluids which present special problems because of their tendency to clog up small diameter tubing of the type usually used to connect to the pressure taps of such pipes. In particular, such problems arise with dirty fluids, those which contain solids, and those which are highly viscous. Examples of applications where such problems occur include measuring the flow of wastewater, pulp stock, and light slurries.
The usual pressure transducer assembly used for measuring pressure differentials in process piping has a pressure receiving body which encloses a measuring transducer and is connected by way of small bore tubing to pressure taps on the pipe. A fill fluid having a low temperature coefficient and little compressibility is used in the passages and cavities of the pressure receiving body and transducer. Typically, the process fluid is isolated from the fill fluid by large barrier diaphragms. These diaphragms deflect in response to the pressure transmitted through the process fluid which fills the small bore tubing, and the fill fluid on the other side of the barrier diaphragms transmits the pressure changes through passages in the pressure receiving body to the measuring transducer.
The measuring transducers may be of several different types, such as a capacitive type, where the diaphragm forms one plate of a differential capacitor; or the strain gauge type, where the diaphragm incorporates or connects with a strain gauge so that the strain resulting from the diaphragm deflection is a measure of the pressure difference across the diaphragm. Typically, the diaphragms may be made of different materials such as stainless steel, single crystal silicon, etc.
When it is desired to measure the pressure differential across a flow restriction in piping for process fluids containing solids, or those which are very viscous, the small bore tubing will tend to clog and thus prevent trouble free measurement.
It is an object of this invention to provide a differential pressure measuring assembly which will make possible flow measurements of dirty fluids, those with solids, and those of high viscosity, particularly in small diameter process pipes, in low range applications, and where temperature compensation is necessary to obtain the desired accuracy.